In both wet-lay and air-lay web forming operations, fibers are conveyed in a fluid stream onto a foraminous surface to form the fibrous web. In commercial installations, it is highly desirable to increase product output to thereby minimize the unit cost of manufacturing, and this is particularly important when manufacturing single and limited use items, such as cosmetic pads, industrial towels, household towels, facial tissues, impregnated wipes, components of disposable diapers and sanitary napkins, etc. Products of this type must be economically manufactured so that they can be sold profitably at a price that is sufficiently low to justify their frequent disposal.
One way of increasing production output in a web forming line is to first form the fibrous web several times wider than the desired width of the final product, and thereafter sever the web in laterally spaced-apart regions to form several web sections from which the product can be formed. This technique can be very advantageously employed in the formation of single and limited use air-lay products that are intended to compete with products made by faster wet-lay processes.
One approach to forming wide webs is disclosed and claimed in U.S. Pat. No. 4,065,832, issued to Rudolf Neuenschwander, and assigned to Scott Paper Company. The preferred apparatus disclosed in this patent includes a foraminous forming surface obliquely oriented to the direction of fiber flow through the conveying duct, and this surface intercepts the downstream end of the duct so that its lateral dimension between laterally spaced-apart duct sidewalls is greater than the width of the downstream end of the duct, as measured in a direction generally normal to the direction of fiber flow through the duct. In the apparatus disclosed in the Neuenschwander patent, a web of the desired basis weight is directly deposited on the obliquely oriented forming surface, and then is conveyed to subsequent post-treatment operations, if desired.
The oblique orientation between the forming surface and the conveying duct establishes an acute angle .alpha. between one of the duct sidewalls and the forming run of the foraminous member, as is clearly shown in FIG. 1 of the Neuenschwander patent. This angular relationship establishes a restricted area adjacent the edge of the duct to cause the formation of a thin edge; especially in thick webs. When it is necessary or desirable for the web to have a substantially uniform thickness across its entire cross-machine-direction, the thin edges must be removed; thereby resulting in production inefficiency. Thus, the apparatus disclosed in the U.S. Pat. No. 4,065,832 is not sufficiently versatile to form webs with a substantially uniform thickness from edge to edge over a wide range of basis weights. The present invention relates to a modification of the system described and claimed in the U.S. Pat. No. 4,065,832, and provides a degree of versatility which the U.S. Pat. No. 4,065,832 system does not possess.